Technical Field
The present disclosure is directed to a leadframe package with a solder wettable sidewall formed using a pre-molded leadframe and methods of manufacturing the same.
Description of the Related Art
A typical semiconductor package includes a die coupled to a leadframe and various electrical contacts. The resulting combination is then covered with an encapsulant to create the package. Lands (also referred to as leads) located on a bottom surface of the package and, in many cases, side surfaces of the package provide electrical connection to a circuit board, such as a printed circuit board (PCB). When coupling the package to the PCB, the packages are mounted directly on the surface of the PCB using surface mount technology (SMT).
Although SMT allows for smaller packages, it also creates some disadvantages. In particular, the solder joints between the package and the PCB can be weakened due to the PCB and the package having different coefficients of thermal expansions (CTE). Thus, the reliability of the package may in some cases depend on the integrity of the solder joints and therefore, stronger solder joints are desired. But, most surface mount leadframes only have solder wettable material on the bottom of the package. The sidewalls of the package are often comprised of material that is incompatible with solder, which results in weak solder joints, or no solder joints, between the PCB and the sidewalls of the package. Finally, in some cases, the force of manufacturing processes in select locations of the thin metal leadframe results in leadframe bouncing, which may cause the thin metal of the leadframe to crack or fracture.
Past responses to these issues have been to add additional elements to the package. These solutions are often cost-prohibitive because adding additional elements increases the number of steps in the manufacturing process, which decreases efficiency and necessarily increases the per unit manufacturing cost of each package. Further, many solutions prevent the package from being inspected by Automatic Visual Inspection (AVI), which can result in lower package reliability and cycle life because the solder joints cannot be properly inspected before leaving the manufacturing facility.
These issues are embodied in a typical semiconductor package 20, as shown in FIG. 1. The package 20 has a metal layer 22 on a bottom surface of certain portions of the package 20. The package 20 also has sidewalls 24 with a first portion 28 comprised of encapsulant and a second portion 26 comprised of lead. As such, when the package 20 is attached to a PCB or other circuit board, no solder joints can be formed between the PCB and the sidewalls 24 because both the encapsulant and the lead are comprised of material that is incompatible with solder. As a result, solder joints cannot be formed between the PCB and the sidewall 24 of the package 20, which reduces the strength of the solder joints in the package 20 and prevents the package 20 from being inspected by AVI. The net outcome is a less reliable package.